Arenaviruses cause chronic infections of rodents across the world, and human infections occur through mucosal exposure to aerosols or by direct contact of abraded skin with infectious materials (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins). Both viral and host factors contribute to a variable outcome of arenavirus infection, ranging from virus control and clearance by the host defenses to subclinical chronic infection, to severe disease (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins). Several arenaviruses cause hemorrhagic fever (HF) disease in humans and pose a serious public health problem in their endemic regions (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins; Bray, 2005, Curr. Opin. Immunol. 17:399-403). Lassa virus (LASV) infects several hundred thousand individuals yearly in West Africa resulting in a high number of Lassa fever (LF) cases associated with high morbidity and mortality (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins; Bray, 2005, Curr. Opin. Immunol. 17:399-403). Recent studies indicate that LASV endemic regions continue to expand with a current population at risk of ˜200 million people (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins; Bray, 2005, Curr. Opin. Immunol. 17:399-403). Hence, with Dengue fever exception, the estimated global burden of LF is the highest among viral HF (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins; Bray, 2005, Curr. Opin. Immunol. 17:399-403).
Notably, increased traveling to and from endemic regions has led to the importation of LF cases into non-endemic metropolitan areas around the globe (Freedman and Woodall, 1999, Med. Clin. North Am. 83:865-883). Likewise, Junin virus (JUNV) causes Argentine HF (AHF), a disease endemic to the Argentinean Pampas with hemorrhagic and neurological manifestations and a case fatality of 15-30% (Peters, 2002, Curr. Top. Microbiol. Immunol. 262:65-74). In addition, evidence indicates that the worldwide-distributed prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen of clinical significance (Barton, 1996, Clin. Infect. Dis. 22:197; Jahrling and Peters, 1992, Arch. Pathol. Lab. Med. 116:489-488). Moreover, because their stability, high morbidity, potential for aerosol transmission and unrestricted source from their natural rodent hosts, several arenaviruses including LCMV, LASV and JUNV represent a credible bioterrorism threat and are considered Category A agents (Borio et al., 2002, J. Am. Med. Assoc. 116:486-488).
There are currently no FDA-approved vaccines against HF arenaviral diseases and current antiviral therapy to combat arenavirus infections is limited to an off-label use of ribavirin. However, ribavirin is only partially effective and has several limitations, including the need of intravenous and early administration for optimal efficacy, and significant side effects (Damonte and Coto, 2002, Adv. Virus. Res. 58:125-155; Jahrling et al., 1980, J. Infect. Dis. 141:580-589; McCormick et al., 1986, N. Engl. J. Med. 314:20-26; Rodriguez et al., 1986, Rev. Argent. Microbiol. 18:69-74). The JUNV live-attenuated Candid1 strain has been shown to be an effective vaccine against AHF (Enria et al., 2008, Antiviral Res. 78:132-139; Enria et al., 1986, Med. Microbiol. Immunol. 175:173-136). However, outside Argentina, Candid1 has only investigational new drug (IND) status and studies addressing long-term immunity and safety have not been conducted. Moreover, Candid1 does not protect against LASV.
Despite significant efforts dedicated to the development of LASV vaccines, not a single LASV vaccine candidate has entered a clinical trial although the MOPV/LASV reassortant ML29, as well as recombinant VSV and vaccinia virus expressing specific LASV antigens, have shown promising results (Falzarano and Feldmann, 2013, Curr. Opin. Virol. 3:343-351). Specifically, ML29 exhibited good safety and efficacy profiles in animal models, including non-human primates, of LASV infection (Falzarano and Feldmann, 2013, Curr. Opin. Virol. 3:343-351). However, the high prevalence of HIV within LASV-endemic regions raises safety concerns about the use of VSV- or vacciniabased platforms. Likewise, the mechanisms of ML29 attenuation remain poorly understood and additional mutations, including reversions, in ML29 or reassortants between ML29 and circulating virulent LASV strains, could result in viruses with enhanced virulence.
Nevertheless, the natural history of LASV infection and epidemiological studies in West Africa indicate that a live-attenuated vaccine (LAV) remains the most feasible and attractive approach to control LF (Falzarano and Feldmann, 2013, Curr. Opin. Virol. 3:343-351). Control of LASV infection seems to be mediated mainly by cellular immune responses, and significant titers of LASV neutralizing antibodies (NAbs) are usually observed only in patients who have clinically recovered (Jahrling and Peters, 1984, Infect. Immun. 44:528-233). However, passive antibody transfer has been shown to induce protection in animal models of LF (Jahrling, 1983, J. Med. Virol. 12:93-102) and in limited human studies (Monath and Casals, 1975, Bull. World Health Organ. 52:707-715) suggesting that a vaccine capable of inducing the right combination of cellular and humoral responses might be the preferred candidate. LAV are excellent candidates for the induction of both robust cellular and humoral immune responses following a single immunization (e.g. influenza), which would be desirable for vaccine use in rural areas of West Africa.
Arenaviruses are enveloped viruses with a bi-segmented negative-stranded (NS) RNA genome and a life cycle restricted to the cell cytoplasm (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins). Each genomic RNA segment, L (ca 7.3 kb) and S (ca 3.5 kb), uses an ambisense coding strategy to direct the synthesis of two polypeptides in opposite orientation, separated by a non-coding intergenic region (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins). The S RNA encodes the viral glycoprotein precursor (GPC) and the viral nucleoprotein (NP). GPC precursor is co-translationally cleaved by signal peptidase to produce a stable 58 amino acid stable signal peptide (SSP) and GPC that is post-translationally processed by the cellular site 1 protease (SIP) to yield the two mature virion glycoproteins GP1 and GP2 that form the spikes that decorate the virus surface (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins). GP1 is located at the top of the spike and mediates virus receptor recognition and subsequent cell entry via endocytosis, whereas GP2 mediates the pH-dependent fusion event required to release the virus ribonucleoprotein core into the cytoplasm of infected cells (Buchmeier et al., 2007, Ch. 50, pgs. 1791-1827 in Fields Virology Vol. II, Lippincott Williams & Wilkins). The L RNA encodes the viral RNA dependent RNA polymerase (L), and the small RING finger protein Z that has functions of a bona fide matrix protein (Perez et al., 2003, Proc. Natl. Acad. Sci. U.S.A. 110:9481-9486; Strecker et al., 2003, J. Virology 77:10700-10705).
The inability to genetically manipulate the arenavirus genome has hampered studies aimed at understanding its molecular and cell biology, as well as pathogenesis, and the ability to generate attenuated arenaviruses for vaccine development. Reverse genetics systems for the prototypic arenavirus LCMV have been developed (Emonet et al. 2011, J. Virology 85:1473-1483; Lee and de la Torre, 2002, Curr. Top. Microbiol. Immunol. 262:175-193). Subsequently, reverse genetics approaches for a variety of arenaviruses, including JUNV and LASV, have been developed (Emonet et al. 2011, J. Virology 85:1473-1483; Lee and de la Torre, 2002, Curr. Top. Microbiol. Immunol. 262:175-193; Albarino et al., 2009, J. Virology 83:5606-5614; Albarino et al., 2011, J. Virology 85:4020-4024; Ortiz-Riano et al., 2013, J. Gen. Virology 94:1175-1188). These systems have resulted in a novel and powerful tool for the investigation of the viral cis-acting sequences and proteins, both viral and cellular, that control cell entry, RNA replication, gene expression, assembly and budding of arenaviruses. Importantly, recombinant infectious arenaviruses with predetermined mutations in their genomes can be rescued and their phenotypes can be examined both in cultured cells and in validated animal models of infection (Emonet et al. 2011, J. Virology 85:1473-1483; Ortiz-Riano et al., 2013, J. Gen. Virology 94:1175-1188; Cheng et al., 2013, J. Vis. Exp. 78:doi: 10.3791/50662). Recombinant tri-segmented arenaviruses have been developed that permit the generation of recombinant arenaviruses expressing additional genes of interest (Ortiz-Riano et al., 2013, J. Gen. Virology 94:1175-1188; Cheng et al., 2013, J. Vis. Exp. 78:doi: 10.3791/50662; Emonet et al., 2011, Virology 411:416-425; Emonet et al., 2009, Proc. Natl. Acad. Sci. U.S.A. 106:3473-3478) as well as single-cycle infectious, reporter-expressing, recombinant LCMV in which GPC is replaced by GFP (rLCMVAGPC/GFP) (Rodrigo et al., 2011, J. Virol. 85:1684-1695). Genetic complementation with plasmids or stable cell lines expressing arenavirus GPCs of interest produces the corresponding GPC-pseudotyped rLCMVΔGPC/GFP that can be used to assess NAb responses to HF-causing arenaviruses using a Biosafety Level 2 (BSL2) platform (Rodrigo et al., 2011, J. Virol. 85:1684-1695).
Thus, there is a need in the art for an effective LAV therapy which protects against arenavirus associated diseases and disorders. The present invention addresses this unmet need in the art.